Ultra high frequency amplifier system



- Oct. 25, w BROWN ULTRA HIGH FREQUENCY AMPLIFIER SYSTEM Filed April 12, 1945 3| DRIVING SOURCE INVENTOR WILLIAM T. BROWN ATTOR NEY Patented Oct. 25, 1949 ULTRA HIGH FREQUENCY AMPLIFIER SYSTEM William T. Brown, Fort Wayne, Ind., assignor, by

mesne assignments, to Farnsworth Research Co p rati n, a corp r i n. of In i na Application April; 12, 1945, Serial No. 588,010

5, Claims. 1

This invention relates to amplifier systems and particularly to push-pull amplifying stages adapted for ultra-high frequency transmitters.

The advantages of a push-pull amplifier are well known to those skilled in the art. Amplifiers of this type deliver a greater output particularly at high and ultra-high frequencies. Another advantage of a push-pull amplifier is that the capacitances of the thermionic tube electrodes are connected in series and thus minimized. It has already been suggested to use a push-pull connected amplifier as the power amplifying stage of a modulated carrier wave transmitter. To this end the input circuit of two push-pull connected thermionic tubes is formed by a pair of parallel straight conductors connected to the two grids of the tubes and short-circuited at the far end. The output circuit is constituted by another pair of straight conductors connected to the plates of the two tubes and short-circuited at the far end. In order to obtain still larger outputs, particularly at ultra-highirequencies, it is desirable to use more than one pair of tubes connected in pushpull. In that case the problem arises how to connect, for instance, two pairs of tubes in such a manner that the interelectrode grid and plate capacitances of the thermionic tubes are minimized.

It is an object of the present invention, therefore, to provide a push-pull amplifier system suitable for amplifying signals at ultra-high frequen-- cies.

Another object of the invention is to provide ultra-high frequency amplifying stages where a plurality of thermionic tubes are connected in H push-pull parallel circuits in a manner to reduce the plate and grid'capacitances of the tubes.

In accordance with the present invention, there is provided an amplifier for ultra-high frequencies comprising twopairs of thermionic devices each including a grid and an anode. Resonant grid circuits are provided each interconnecting the grids of one pair of the the m onic devices as well as resonant anode circuits each interconnecting the anodes of one pair of the thermionic devices. Means are provided for coupling a common driving source to the grid circuits and further means for coupling a common utilization device to the anode circuits.

For a better understanding of the invention, together with other and further objects thereof, reference is made to he followin scription. taken in connection with the a comp ny n drawing. and its SGO e will be pointed out in the appended claims.

In the accompanying drawing, the single figure is a schematic representation in perspective of an amplifier system embodying the present inven tion.

Referring now more particularly to the single figure of the drawing, there is shown an amplifier system including thermionic vacuum tubes I, 2, 3 and 4. Thermionic tubes l to 4 comprise, respectively, cathodes 5, 6, 1, 8, grids 10, H, l2, l3 and anodes |4, |5, i6 and I1. Grids I0 and II are. interconnected by resonant conductor 20, while resonant conductor 2| interconnects grids l2 and I3. Conductors 20 and 2| are arranged in paral-l 161 and form a two wire transmission line. Similarly, anodes I4 and H: are interconnected by resonant conductor 22 and anodes l6 and I! are interconnected by resonant conductor 23, conductors 22 and 23 being arranged in parallel and forming a two-wire transmission line.

Grid conductors 20 and 2| have their mid points short-circuited by cross bar or bridging member 25. Similarly, anode conductors 22 and 23 have their mid points short-circuited by cross bar or bridging member 26. Variable tuning condensers 21, 28, 29 and 39 may be shunted across grid transmission line 20, 2| and anode transmission line 22, 23, respectively. Tuning condensers 21 to 30 serve for tuning grid transmission line 20, 2| and anode transmission line 22, 23 to a predetermined wave length. However, they are not essential to the operation of the amplifier system of the invention and hence may be omitted.

Preferably, the section of each of the four conductors 20, 2| 22 and 23 arranged between bridging members 25 and 26, respectively, and its associated electrode has an effective length equivalent to a quarter-wave length of the carrier wave or signal to be amplified, as indicated in the drawing. However, the efiective length of each of the eight sections of conductors 2|, 22, 23 and 24 may also be equivalent to an odd multiple of a quarter-wave length. The total effective length of each of the four conductors 2|, 22, 23 and 24, therefore, is equivalent to a half-wave length or an odd multiple thereof. It should be understood, however, that due to the effect of the capacitances of grids Hi to l3 and the capacitances of condensers 21 to 3|! the physical length of conductors 2|, 22, 23 and 24 should be less than a half-wave length or an odd multiple thereof in order to make the equivalent length of the conductors equal to a half-wave length multipled by an odd n mber.

A driving source, schematically indicated at 3|,

is coupled by coupling bar 32 to bridging member 25 in the manner of a transformer coupling. A load or utilization device, schematically represented by dipole antenna 33, is coupled similarly by coupling bar 34 to bridging member 26. The four cathodes 5, 6, 1 and 8 are connected to a common reference potential such, for example, as ground. Each cathode has been shown connected individually to ground. Actually, however, cathodes 5 to 8 may be kept at ground potential by means-of a suitable transmission line connected toground which, for instance, may have a length between ground and each cathode equivalent to a half-wave length or a multiple thereof. The negative grid biasing voltage may be supplied to bridging member 25 through lead 35, as shown schematically. Similarly, the positive anode potential may be supplied through lead 36 to bridging member 26.

The amplifier system of the invention operates as follows. Transmission line 20, 2| is equivalent to resonant circuits interconnecting grids l0, ll, l2 and I3. Driving source 3| is coupled to bridging member 25 in the manner of a transformer coupling. Hence, grids I and I3 are in phase opposition as well as grids II and I2. Furthermore, a standing wave is developed in conductor 20 at its resonant frequency. Thus, the standing voltage wave has a nodal point at the connection of conductor 20 to bridging member 25. The ventral sections or antinodes of the standing voltage Wave occur at grids II] and II and, hence, it will be seen that grids l0 and H are also in phase opposition. The standing voltage wave developed in conductor 2| also has its nodal point at the center point thereof, while the ventral sections or antinodes are at the far ends, that is, at grids l2 and I3. Accordingly, tubes l and 3 are in phase with one another and so are tubes 2 and 4. On the other hand, tubes 2 and 4 are in phase opposition with respect to tubes l and 3. The cycle of operation is such that at a certain instant tubes l and 3 will conduct space current, while tubes 2 and 4 are biased to cut: off. After a certain time interval tubes l and 3 will be biased to cut-off, while tubes 2 and. 4 conduct space current. Hence, two of the four tubes l, 2, 3 and 4 are always operating in parallel.

By virtue of the fact that conductors 20 and 2| have an effective length from bridging member 25 to their respective electrodes equivalent to a quarter-wave length multiplied by an odd. number, a small voltage impressed on bridging member 25 will result in a high voltage at grids I0, H, l2 and I3. This is due to the fact that a quarter-wave transmission line functions as an impedance inverting network. In a similar manner, the load or utilization device coupled to bridging member 26 should have a low impedance so that plates [4, I5, l5 and [1 look into a high impedance.

In some cases it may be desirable to utilize an impedance matching network between driving source 3| and its coupling bar 32, as well as between the utilization device, such as dipole antenna 33, and its coupling bar 34.- Such an impedance matching network may take the form of a quarter-wave transmission line of suitable impedance.

It is to be understood that driving source 3| may, for instance, be directly connected to grid transmission line 20, 2|. Similarly, dipole antenna 33 could be directly connected to anode transmission line 22, 23 instead of being coupled 4 thereto. One of the main advantages of the amplifier system of the invention is that the grid and plate capacitances of tubes I, 2, 3 and 4 are minimized. On the other hand, a larger output may be obtained because at any instant two of the four tubes are connected in parallel, both conducting space current. The amplifier system of the invention is noteworthy for its high degree of symmetry which is always an important consideration in ultra-high frequency circuits.

While there has been described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the invention, and it is, therefore, aimed in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. An amplifier for ultra-high frequencies comprising two pairs of thermionic devices each including a grid and an anode, two grid conductors forming a resonant two-wire transmission line, each of said grid conductors interconnecting the grids of one pair of said devices for maintaining them in phase opposition, a first bridging member for short-circuiting the center points of said grid transmission line, two anode conductors forming a resonant two-wire transmission line, each of said anode conductors interconnecting the anodes ofone pair of said devices, a second bridging member for short-circuiting the center points of said anode transmission line, a driving source coupled to said first bridging member, and a utilization device coupled to said second bridging member.

2. An amplifier for ultra-high frequencies comprising two pairs of thermionic devices each including a grid and an anode, two grid conductors forming a resonant two-wire transmission line, each of said grid conductors interconnecting the grids of one pair of said devices for maintaining them in phase opposition, a first bridging member-for short-circuiting the center points of said grid transmission line, two anode conductors forming a resonant two-wire transmission line, each of said anode conductors interconnecting the anodes of one pair of said devices, a second bridging member for short-circuiting-the center points of said anode transmission line, said transmission lines being substantially resonant to the same frequency, means for coupling a driving source to said grid transmission line, and means for coupling a common utilization device to said anode transmission line.

3. An amplifier for ultra-high frequencies comprising two pairs of thermionic devices each having a grid, an anode and a cathode, said cathodes being connected to a common reference potential, two grid conductors forming a resonant two-wire transmission line, each of said grid conductors interconnecting the grids of one pair of said devices for maintaining them in phase opposition, a first bridging member for short-circuiting the center points of said grid transmission line, two anode conductors forming a resonant two-wire transmission line, each of said anode conductors interconnecting the anodes of one pair of said devices, a second bridging member for short-circuiting the center points of said anode transmission line,. said transmission lines being substantially resonant to the same frequency, a driving source coupled to said first bridging member, and

a utilization device coupled to said second brid ing member.

4. An amplifier for ultra-high frequencies comprising two pairs of thermionic devices each including a grid electrode and an anode electrode, two grid conductors forming a two-wire transmission line, each of said grid conductors interconnecting the grids of one pair of said devices, a first bridging member for short-circuiting the center points of said grid transmission line, two anode conductors forming a, two-wire transmission line, each of said anode conductors interconnecting the anodes of one pair of said devices, a second bridging member for short-circuiting the center points of said anode transmission line, the effective length of each conductor from its center point to its associated electrode being substantially equal to a quarter-wave length of the signal to be amplified multiplied by an odd number, means for coupling a driving source to said grid transmission line, and means for coupling a utilization device to said anode transmission line, whereby said 'pairs of thermionic devices are connected in push-pull.

5. An amplified for ultra-high frequencies comprising two pairs of thermionic devices each having a grid electrode, an anode electrode and a cathode, said cathodes being connected to a common reference potential, two grid conductors forming a two-wire transmission line, each of said grid conductors interconnecting the grids of one pair of said devices, a first bridging member for short-circuiting the center points of said grid transmission line, two anode conductors forming a two-wire transmission line, each of said anode conductors interconnecting the anodes of one pair of said devices, a second bridging member for short-circuiting the center points of said anode transmission line, the effective length of each conductor from its center point to its associated electrode being substantially equal to a quarter- Wave length of the signal to be amplified multiplied by an odd number, a driving source coupled to said first bridging member, and a utilization device coupled to said second bridging member, whereby said pairs of thermionic devices are connected in push-pull.

WILLIAM T. BROWN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,796,486 Southworth Mar. 17, 1931 1,912,191 Green May 30, 1933 2,048,751 Mathiev July 28, 1936- 2,064,481 Mathiev Dec. 15, 1936 2,266,197 Hansell Dec. 16, 1941 2,340,352 Watts Feb. 1, 1944 

